Value of standard electrode potential for the oxidation of Cl- ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why is Cl- oxidised at anode instead of water?
Under the condition of electrolysis of aqueous sodium chloride, oxidation of water at anode requires over potential. So, Cl- is oxidized at anode instead of water. Possible oxidation half cell reactions occurring at anode are
Species having lower cell undergo oxidation first than the higher value but oxidation of H2O to O2 is kinetically so slow that it needs some overvoltage.
